Excerpt from Dr Wentz's article Do you have Hypothyroidism or Hashimoto’s or Both?...
"Most cases of hypothyroidism in the United States, Canada, Europe, and in most countries that add iodine to their salt supply are caused by Hashimoto’s, an autoimmune condition. Depending on the source, estimates are that between 90-97% of those with hypothyroidism in the United States have Hashimoto’s.
That is a big fat yes! lol. Most cases of Hashi's have positive thyroid antibodies. Ask your doctor for thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb).
I agree that most cases of hypothyroidism that are DIAGNOSED are due to Hashi's but that is only because of the current standard of care for hypothyroidism, which is totally reliant on the TSH test. When TSH is over the range, and a followup Free T4 test is below its range, then that is diagnosed as hypothyroidism. Along with that, tests would be done for the antibodies of Hashi's. Those tests are TPO ab and TG ab.
Patients whose TSH is over range, but Free T4 is within range are told they have subclinical hypothyroidism and no treatment is required, at least at that time. But there is also a huge number of people with hypothyroidism that go undiagnosed. Although vital, symptoms and Free T3 level are typically ignored. If the patient has central hypothyroidism of course it is not identified by these measures. As a result of this inadequate standard of care, even the American Thyroid Association has stated that over 20 million Americans have thyroid disease and that up to 60% are unaware of their condition. And I think this is an under statement.
Diagnosis for possible hypothyroidism should start with a full medical history, followed by an evaluation for signs/symptoms that occur more frequently with hypothyroidism, and then extended biochemical testing to support prior findings. Hypothyroidism is correctly defined as "insufficient T3 effect in tissue throughout the body, due to inadequate supply of, or response to, thyroid hormone. " Insufficient T3 Effect can be due to a number of different processes and variables. So there is no biochemical test that can be used as a pass/fail decision about hypothyroidism.
If the history, evaluation for signs/symptoms, and followup testing indicate the likelihood of hypothyroidism then there should follow a therapeutic trial of thyroid med adequate to raise the Free T4 and Free T3 levels and determine the effect on symptoms. Along with that the important variables like cortisol, Vitamin D, B12 and ferritin should be tested and supplemented as needed to optimize. Note that dosage should never be determined based only on TSH, but instead based on symptom relief. So, if the diagnosis of hypothyroidism is confirmed then thyroid hormone replacement dosage should be adjusted so as to eliminate the signs/symptoms of hypothyroidism without creating any signs/symptoms of hyperthyroidism. A recent, excellent scientific study concluded that: " Hypothyroid symptom relief was associated with both a T4 dose giving TSH-suppression below the lower reference limit and FT3 elevated further into the upper half of its reference range." To achieve those adequate Free T3 levels frequently requires addition of a T3 source to your meds.